1. Field of the Invention
The present invention relates generally to moveable stages for use in focused beam systems; and more particularly to a high speed rotational stage in conjunction with a linear stage to form a high speed scanning system without scanning the beam, allowing a large area specimen to be imaged with a substantially higher speed using an optimally focused beam.
2. Description of the Prior Art
In the context of scanning microscopy, the most common image formation systems in the prior art make use of Cartesian raster scanning to form an image. In a typical imaging system, a source of energy such as an electron beam, ion beam or photon beam is used to irradiate a specimen. The interaction between the source beam and the specimen produces a signal that can be detected which corresponds to the signal intensity at the interaction point. There are two Cartesian raster scanning mechanisms commonly used to form an image: (1) a beam scanning system wherein the source beam is Cartesian raster scanned over the area of interest of a static specimen; (2) a stage scanning system wherein the specimen is mounted on a mechanical Cartesian scanning stage, and the stage is scanned with respect to the static source beam to cover the area of interest.
In a beam scanning system, the source beam is typically scanned from left to right in a raster manner, pixel by pixel, before xe2x80x98flying backxe2x80x99 to the beginning of the next line. This process repeats from the top to the bottom for a complete image acquisition before returning to the top of the scan again. In a stage scanning system, the mechanical scanning stages scan from left to right in a raster manner using stepper motors, servo motors or voice coils. These two methods impose significant problems and limitations. Firstly, both methods need a fly-back at the end of each line scan, which slows down the image acquisition. For the stage scanning system, the relatively large mass of the mechanical stage needs significant settling time, which further slows down the rate of image acquisition. In addition to this, the beam scanning system suffers from aberrations when the beam is deflected from the optical axis while scanning a relatively large area. This is a serious drawback of the beam scanning system when scanning a large area.
In conclusion, a mechanical scanning stage with high speed capability for large area specimen scanning would have advantages in many applications.
It is, therefore, an object of the present invention to provide a mechanical scanning stage for high speed image acquisition in a focused beam system.
It is another object of the present invention to provide a mechanical scanning stage that can achieve high speed image acquisition of a large area specimen.
Briefly, a preferred embodiment of the present invention includes a mechanical scanning stage for high speed image acquisition in a focused beam system. The mechanical scanning stage preferably is a combination of four stages. A first stage provides linear motion. A second stage, above the first stage, provides rotational positioning. A third stage above the rotational stage is moveable in a first linear direction, and the fourth stage above the third stage is positionable in a second linear direction orthogonal to the first direction. The four stages are responsive to input from a controller programmed with a polar coordinate pixel addressing method, for positioning a specimen mounted on the mechanical stage to allow an applied static focus beam to irradiate selected areas of interest, thereby imaged by collecting signals from the specimen using a polar coordinate pixel addressing method.